A heat recovery means serves for the recovery of energy from heat or respectively from waste heat. This waste heat can originate for example from an internal combustion engine, in particular from the exhaust gas of an internal combustion engine. Usually, the heat recovery means has a circuit for the recovery of the energy, in which a working medium circulates and in which there are arranged in succession a conveying means for conveying the working medium, an evaporator for evaporating the working medium, an expander for expanding the working medium and a condenser for condensing the working medium. The conveying means therefore conveys the working medium in the circuit, which is evaporated in the evaporator via the waste heat for example of the exhaust gas, and therefore receives energy which is converted in the expander. The thermal energy which is received via the evaporator is therefore converted in the expander into a mechanical energy which can be picked up in the form of a torque at the expander.
Different modes are present during operation of the heat recovery means. Between the different modes, in particular different thermodynamic states are present, which differ in particular through different aggregate states of the working medium in the circuit. On starting of the heat recovery means, for example a start-up operation prevails, whereas on or respectively after switching off the heat recovery means, a shutdown operation prevails.
For an independent operating of the heat recovery means, it is basically conceivable to separately drive the conveying means for conveying the working medium. In this case, the conveying means can be present as an independently driven pump. Accordingly, the conveying means can be adapted to the respective operation of the heat recovery means, in particular the start-up operation and the shutdown operation can be regulated in a simplified manner. The use of such an independent conveying means, however, has the disadvantage that the overall energy efficiency of the heat recovery means is reduced.
To improve the overall energy efficiency of the heat recovery means, it is conceivable to connect the conveying means with the expander in such a way that the conveying means is driven by the expander. This indeed leads to said improvement in the energy efficiency. As the expander does not make available a sufficient torque for driving the conveying means, in particular in the start-up and/or shutdown operation, a sufficient adaptation of the conveying means can not be undertaken in these operating modes. To solve this problem, it is conceivable to use in the circuit a, usually electrically driven, auxiliary conveying means, which supports the conveying means or replaces it in particular operating modes. The use of the auxiliary conveying means leads, however, to a reduction in the overall energy efficiency of the heat recovery means. Furthermore, additional components are necessary, which increase the production costs and the installation expenditure of the heat recovery means.
The present invention is therefore concerned with the problem of indicating for a heat recovery means of the type named in the introduction, and for methods for operating such a heat recovery means, improved or at least alternative embodiments, which are distinguished in particular by an increased energy efficiency and/or a reduced installation expenditure.
This problem is solved according to the invention by the subjects of the independent claims. Advantageous embodiments are the subject of the dependent claims.